The invention over which the disclosed apparatus and method is an improvement is that which is described in U.S. Pat. No. 3,212,411, issued to Robert S. Storms on Oct. 19, 1965. In that patent a disc of polytetrafluoroethylene (PTFE) was hot-formed onto a piston. When so formed, the piston's periphery received a low coefficient of friction outer surface so as to enable its unrestricted reciprocation within a fluid cylinder. With subsequent incremental improvements in the Storms invention, it soon became the standard for shock absorbers and McPherson struts used in automotive suspension systems. Specific ones of those improvements related to the use of V-grooves with lands between adjacent grooves in the piston and the addition of an anchoring groove at the end of the piston from which the PTFE is applied. This anchoring groove enabled use of a relatively flat washer with a central hole or opening, instead of the cup-shaped blank shown in the '411 patent. The hole was cold-expanded and snapped over a retaining ring at the end of the piston. The washer thus became affixed to the piston, enabling the anchoring groove to hold it tightly in place as it was hot-formed toward the opposite end of the piston to take the piston's cylindrical shape and, in effect, become its outer anti-friction surface. Notwithstanding these improvements, and despite the fact that they are quite adequate when used in conventional automotive shock absorbers, new problems became apparent when many automobile manufacturers began producing front wheel drive vehicles. This led to a more sophisticated shock absorber design generally referred to as a "strut", more commonly called the well-known McPherson strut.
Not only is the suspension system of a front wheel drive vehicle subjected to much more severe shock loading than rear shocks, but of necessity, a front suspension system must enable proper steering of a rapidly bouncing set of wheels. A shock transmitted through a front wheel when hitting a "chuck hole" is considerably more noticeable than one received by a rear wheel, for example. It is obvious the front wheels must maintain contact with the road surface for best and safest steering. Also, the temperatures at which such front wheel drive struts normally operate, especially in hot climates during summer operation, can be quite high. Constant and rapid piston action on a rough road, especially at relatively high temperatures, required consideration. Since hot-forming does not bond the PTFE to the piston outer surface, a severe shock load could cause blow-by, or a "popping" of the band from the piston. Even without much band wear, blow-by can occur if the pressure is excessive. Naturally, once a band is disconnected from the piston, the hydraulic shock absorber or strut is rendered totally useless to perform its intended function.